Laminar circuit assmebly



Feb. 27, 1968 LE ROY A. PRoHoFsKY 3,371,249

LAMINAR C IRCUIT ASSEMBLY Original Filed March 19, 1962 2 Sheets-SheetAl INVENTOR. LEROY A. PROHFSKY LE ROY A. PROHOFSKY LAMLNAR cmuur'lASSEMBLY 2 Sheets-Sheet z Feb. 27, 1968 Original Filed March 19, 1962PREPARATION OF BASE MATERIAL APPLY CONDUCTIVE COATING TO BASE MATERIALREMOVAL OF SELECTED PORTIONS OF COATING STACKING OF THE CIRCUIT CARDSINSERTION OF INTERSLIJCTING 59 Nimm -a 4v,

I wpf-...Ilnhn 56' A l 'N I 36| IMMERSION IN MOLTEN SOLDER INVENTOR.LE'RY A. PROHFSKY United States Patent Oiiice 3,371,249 LAMINAR CIRCUITASSEMBLY Le Roy A. Prohoisky, Minneapolis, Minn., assignor to SperryRand Corporation, New York, N.Y., a corporaof Delaware This inventionrelates generally to a multilayer circuit assembly and is a division ofcopending application Ser. No. 180,685 led Mar. 19, 1962, and now PatentNo. 3,187,426. y

Printed circuits are well known in the art and are extensively used inthe electronics industry. Recent trends in the industry towardminiaturization of electronic devices have resulted in a variety ofprinted circuit packaging schemes for arranging a compact circuitassembly. Because modern complex electronic equipment requires unitizedconstruction permitting ease in assembly and maintenance, todayspackaging concepts emphasize modular construction, and these conceptshave been extended to include printed circuit assemblies. For example,in one scheme, the printed circuit card is reduced in size and severalcards are assembled in stacked or superimposed relation. Accompanyingthis method of arranging printed circuit cards in stacked relationshipis the problem of electrically interconnecting the cards. Efforts tominimize spacing between the stacked cards have been limited by themethod used to interconnect the circuitry of the various stacked cards.Though circuit and component sizes may be reduced, the number ofinterconnections required remains the same. Consequently, a reduction insize of the circuit card results in an increased density ofinterconnecting points. Thus major factors limiting the degree ofminiaturization which may be achieved by stacking printed circuit cardsare the means and method used to electrically interconnect the cards.

Two interconnecting methods employed in the past were point-to-pointwiring and the use of edge connecting devices. Point-to-point wiring isundesirable in that in a miniaturized assembly of stacked cards,reliable connections between the cards are extremely difficult andexpensive to make and are subject to serious error. Edge connectingdevices are undesirable in that they necessitate the disposition of theterminal portions of card circuitry along at least one of the cardperimeters and also require the cards to be suiciently spa-ced apart toappropriately accommodate the connecting means. Use of edge connectingdevices also results in increased cost, increased weight of theassembly, and increased bulk as a result of the necessary connectorharness. An inspection of the prior art reveals that eiorts to minimizethe distance between the printed circuit cards forming the stackedassembly have been frustrated by the limited methods presently availablefor interconnecting the cards. The present invention provides a newmultilayer printed circuit assembly, and a new method and means to makeelectrical connections between the assembly layers. The inventionprovides a soldering method for electrically and mechanicallyinterconnecting the stacked printed circuit cards while permittingminimum spacing between the cards and between interconnecting points.The invention permits a reduction in the volume of a multilayer printedcircuit assembly and allows increased density of interconnecting points.

This is accomplished in accord with the present invention by providingin each card a predetermined arrangement of plated-through holes, anddisposing appropriate circuitry in the form of conductive strips on oneface of the card, the conductive strips terminating at the plated-3,371,249 Patented Feb. 27, 1968 through holes. The cards are arrangedin stacked relationship, the hole pattern of each card 'being alignedwith the hole pattern of the other cards. The cards are maintained insuch aligned stacked arrangement by means of a compression type jig orfixture. After the cards have been secured in a fixed relationship, amasking device is disposed about the perimeter of the stack.Subsequently an interconnecting means in the form of a wire wick isinserted in each aligned series of holes, the wick being frictionallyretained within the holes and having its terminal portions extendingoutwardly from the bottom and top of the stack. The entire assembly isthen immersed in a molten solder bath approximately to the top of thestack. The solder is prevented from ilowing over the top card orinwardly between the cards of the stack at the perimeter thereof by themasking device. Solder, under the iniiuence of capillary action anddisplacement forces, ascends each wick and the space between the wickand the metallic walls, and is thereby disposed upon the walls of thehole and the wick, and upon cooling, the solder forms a mechanical andelectrical interconnection. By exposing a portion of the vbase orsubstrate material which is nonsolder wettable, solder ascending thewick is prevented from llowing between the cards in a directiontransverse to the wick. Solder, due to its high surface tension,constricts in the area of the exposed base material.

In a preferred embodiment of the product of the method of thisinvention, the multilayer circuit assembly is used in the modularIconstruction of a logic circuit system. The wicks are fitted withfemale connectors which are received by a housing. Mating with thefemale connectors are the male pins of logic circuit modules. The logiccircuitry is selectively interconnected by the wicks and card circuitry.

Accordingly, it is an object of the present invention to provide amethod for electrically and mechanically interconnecting a multilayerprinted circuit assembly whereby the distance between adjacent printed-circuit cards may be minimized.

It is a further object of this invention to providea method forelectrically and mechanically interconnecting a plurality of closelyspaced, superimposed printed circuit cards in a single, solderingoperation.

It is also an object of this invention to provide a method and means forcompactly arranging a plurality of printed circuits, such method andmeans also permitting increased density of electrical connecting points.

It is also an object of this invention to provide a printed circuitmultilayer assembly wherein the circuit layers are firmly securedrelative to one another without end orI side supporting devices.

It is a still further object of this invention to provide a modularlyconstructed circuit assembly.

These and other more detailed and specific objectives will be disclosedin the course of the following specification, reference being made tothe accompanying drawings, in which:

FIG. 1 is a perspective view of a multiapertured, singlelayered printedcircuit card of the type used in the present embodiment, a small portionof the card being shown in cross-section;

FIG. 2 is a cross-sectional side view of an exemplary stack of printedcircuit boards arranged in accordance with the method of this invention,such stack being shown disposed in a molten solder bath;

FIG. 3 is an enlarged cross-sectional sideI View of a portion' of astack of printed circuit cards, such portion including a single alignedseries of apertures having an interconnecting means soldered to thecoating on the aperture walls; f

FIG. 4 is a ilow chart illustrating a preferred process vforelectrically and mechanically.interconnecting a printedv circuitmultilayer assembly;

FIG. a illustrates in cross-sectional side view a small portion of acircuit card after the coating step of this method has been completed,the back portion of the aperture being removed for clarity inillustration;

FIG. 5b is a View of the FIG. 5 illustration after the coating on thebottom portion of the circuit card Ihas been partially removed; y

FIG. 5c is a view of the FIG. 5b illustration after removal of portionsof the coating within the aperture on the printed circuit card; l

FIG. 6 is a perspective view of a modularly constructed circuit assemblyemploying the printed circuit assembly formed in accordance with themethod of this invention.

Referring now to FIG. 1, there is seen a multi-apertured circuit card 20which includes an insulating base material 22 and a plurality ofconductive strips 26, 28 and 30. The printed circuit base material 22 ispreferably a ceramic material having a thickness of about 0.062 inch.However, other heat resistant material such as epoxy resins, may be used:as a base material. Preferably the selected base material is solderrepellent. The expression solder repellent base material is used hereinto identify a material that will not readily lend itself to wetting bysolder.

An acceptable ceramic is yFotoceram material, a product of Corning GlassWorks, Inc. which is characterized for its high temperature resistanceand etching qualities. Inpreparation, apertures, such as the apertures24, are etched in the base ceramic in accordance with a predeterminedarrangement. In the instant embodiment the aperture pattern isdevelopedby etching the base ceramic material to form the apertures 24 at theintersections of lines forming a 0.10 inch grid. No limitation isintended by the mention of a 0.10 inch grid. Apertures having a diameterof about 0.016 inch have been formed on a 0.035 inch grid pattern. Agrid pattern distribution of the apertures was chosen because in thelight of the several parameters considered, such an arrangement permitsthe formation of a maximum number of apertures. The apertures 24 in theinstant embodiment have an approximate diameter of 0.052 inch; however,.any suitable combination of aperture diameter and wire diameter may beutilized. The -desi-red configuration of printed wiring, such asconductive strips `26, 28 and 30 each having a thickness of the order of0.005 inch, is formed on one side of the card 20 by etc-hing.` Thesestrips terminate at the apertures 24 as exemplified at 26a `and 26b. Thefabrication of the electrically conductive portions of the circuit cardmay be accomplished in any one of several conventional ways and willhereinafter be explained in greater detail. Surrounding each aperture 24is .a small annular metallic ring 34 which is preferably formed of thesame material as the conductive strips. The ring 34 is preferablyintegral with the metallic coating 32 deposited on the aperture walls.

Referring now to FIG. 2, there is seen a stacked plurality of circuitlayers 20a, 2011, 20c, and 20d. Four circuit layers have been chosen forexemplifying the embodiment herein, although as many as sixteen 0.062inch thick circuit layers have been soldered simultaneously by themethod taught by this application. The circuit cards 20a, 2Gb, 20c, and20d are substantially identical with circuit 'card 20 with the exceptionthat the different layers will exhibit a different pattern of conductivestrips. Usually a cover plate (not shown) having the same constructionas the circuit cards except that it has no conductive strips, is placedon top of the uppermost circuit card, in this case card 20d, forprotecting the top circ-uit card and its associated circuitry.Preferably circuitry is located only on one side of each card. However,by utilizing alternate cards as spacers only, circuitry could bedisposed on either or both sides of the circuit cards.

' The aperture pattern is normally the same for each layer, and thelayers are superimposed with the apertures 'of 'each individual layer inregistration with the apertures of ythe adjacent layer. Thus, an alignedseries of apertures,

for example, the series of apertures 24a, Zlib, 24C and 24d is formed byappropriately locating the various layers formed in the stack. Aninterconnecting member or wicking means 36 is disposed through analigned series of apertures such that its ends 37 and 39 projectoutwardly from the apertures. In the specifically identified apertureseries a wick was not shown for clarity in illustration. Preferably themember 36 is in the form of a stranded wire having a diameter slightlyless than the diameter of the apertures. To prevent the wire fromslipping through a series of apertures, it may be bent or distortedslightly. Upon disposition of the wire lin a series of apertures, thebent portion of the wire frictionally engages a portion of the platedcoating 32 on the aperture walls with sufficient force to secure thewire in the desired position. The superimposed cards may be secured instacked relationship by means of a C-clamp (not shown) or the like. p

After the cards have been stacked and secured in adjacent relationship,.a dam 38 is disposed about the periphery of the stack. The dam mayconsist of a silicon rubber compond or other heat resistant material andmay be secured or held against the stack assembly by means of a clampingdevice 42, which extends yabout the periphery of the stack. The darn 38is used as a masking device to prevent solder from the molten solderbath `d0, in which the stack is immersed, from entering the stackthrough spaces between the layers; such spaces being present because ofthe location of the conductive strips on the surface of the cards. Ifdesired, the strips may be recessed in the cards such that the car-d andstrip surfaces are flush.

FIG. 2 also illustrates the attitude of the stacked cards with respectto the solder bath d0 after immersion of the stack in the bath. Thus itis seen that the uppermost surface 21 of the card 20a is atsubstantially the same level or slightly below the level of the bath.The reason for immersing the stack to such a level in the solder bathwill be discussed more fully hereinafter.

Referring now to FIG. 3 there Acan be seen a continuous solder joint 3Sconnecting the wicking means 36 with the solderable coatings 32a, 32b,32C, 32d of each apertured wall of the individual circuit layers. As isseen, the solder has not only filled any space between the wires formingthe wick, but has also substantially filled the annular-like spacepresent between the wick and the material covering the aperture walls.This particular View has been substantially enlarged to more clearlyillustrate the many practical considerations involved in the describedmethod for selectively interconnecting layers of stacked printed circuitcards. It should be noted that as a practical matter the majority of theaperture 24 edges are somewhat rounded rather than square, for exampleas at 4l. It should also be appreciated that the planar surfaces of eachcircuit card are not perfectly fiat nor is the conductive coatingdeposited uniformly thereon, and that for these reasons the annularspacer or barrier ring 34 surrounding any given aperture may not be inphysical contact with the underside of the circuit layer immediatelyabove it. An exaggerated view of such a :condition is illustrated at theinterfacial spaces formed by circuit layers 20a and 20h and circuitlayers 20c and 20d. It is seen that annular rings 3415 and 34d areseparated respectively some small distance from the bottom surfaces 23and 27 respectively of circuit layers 20a and 20c respectively. Liquidsolder present at the upper level of the annular ring 34b or ring 34d isprevented from flowing outwardly along the surfaces 25 and 29 of circuitlayers 20h and 20d respectively by the method of this invention as willbe seen hereinafter. In an ideal situation, such as is suggested by FIG;2, all of the annular rings would tig tly abut the bottom surface of thenext adjacent circuit layer and thereby provide in eiiect a closed wallcontainer for restricting the solder as it ascends the wicking means 36.As a practical matter,

however, this does not occur. The various circuit layers comprising thestack are not perfectly planar and spaces exist ybetween the layerswhich would allow solder ascending the interconnecting means 36 and theannular space between the means and the aperture walls to flow out*wardly in a direction transverse to the wick and cover the face of thecircuit layer. Uncontrolled transverse solder tlow could cause a shortcircuit between conductive strips present on the particular layer. Forexample, if solder escaped uncontrollably through the space betweencircuit layers 29C and 20d, it could electrically connect conductivestrip 48 with the aperture wall coating 32d. Additionally, escapingsolder could electrically connect two wicks. ln the present inventiontransverse solder flow is controlled by effecting a solder constrictionin the area of the spaces between adjacent circuit layers. It should benoted at this time that the aperture wall is not fully covered with thesolderable coating 32 throughout its entire length. At the lowermostportion of each aperture, the insulating base material, which is notsolder wettable, is exposed. Thus, as ascending solder approaches thespace between two circuit layers, any tendency it may have to flow alongthe surface of one layer 'in a direction transverse to the wick isovercome because of its inability to wet the exposed base materialsurface of the next adjacent circuit layer. Thus it is seen that theselective exposing of the base material causes the solder to constrictor withdraw toward the wick forming a void 5). it is this particularfeature of the invention that lemphasizes one of its extremely practicalaspects. The inability to purchase or economically produce perfectlyflat layers of insulating material having a coating of uniformlyelectrodeposited metal such that when one circuit layer is superimposedupon the other, their surfaces mate so perfectly that no space existstherebetween, would, in the absence of this invention, substantiallypreclude the use of solder immersion techniques for internally joining astack of printed circuit cards.

As is indicated in the flow chart of FIG. 4, the method disclosed hereincommences with step l wherein the apertures 24 are formed in theinsulating base material 22. When using certain types of ceramic basematerial, the apertures may be formed by etching. Preparing suchmaterial for etching may involve a photo process whereby the areas orportions of the base material desired to be etched away a're exposed toa light source through a negative or other suitable light maskingdevice. The light is effective to change the material such that it issusceptible to an acid etchant. Alternatively, of course, the aperturesmay be formed by drilling or punching, as might be the case where aparticular base material does not lend itself to etching. The printedcircuit may also be formed yby molding, the apertures being formedduring the molding process. For example, an epoxy resin could be cast ona mold which is provided with a number of arranged pegs for causing theapertures to form in the epoxy. The pegs may be coated with anon-adherent covering of copper having a predetermined thickness. Thenupon removal of the mold, the copper adheres to the hardened epoxy andforms the coating on the aperture walls. In a photo process as used inpreparing certain types of material for etching, it should be noted thatthe scattering of light rays precludes the etching of perfectly straightwalls. This is one of the reasons that the apertures 24 have roundededges 41 as was illustrated in FIG. 3.

Next step 2 is performed. Subsequent to the base material for etching,it should be noted that the scattering including the aperture walls, iscoated with a layer of an electrically conductive material, such ascopper. The coating process may be readily performed in accordance withwell known electroplating techniques for plating on electricallynonconductive base materials. For example, a chemically deposited layerof copper may be caused to deposit on the surfaces of the circuit layer,this chemically deposited layer later having its thickness increased byelectrodepositing copper thereon. In the instant embodiment, a thinlayer of electrodeposited gold is also selectively deposited over thecopper, such gold later serving as a resist during the etchingoperation. Of icourse, other suitable etchant resists may be used inlieu of gold. The gold electrodeposited on one side of the card is onlypermitted to deposit in those areas where the copper is to remain. Thisis accomplished through the use of plating resists in the manner wellknown in the art.

After the coating step has been completed, step 3 is performed. One sideof the coated card is abradcd for causing the gold etchant resist to beremoved therefrom. This usually results in the removal of some copperalso. The plating resist which was used to cover certain portions of thecopper to prevent gold from depositing therelon is also removed at thistime. The card is next immersed in a ferric chloride etching solutionwhere all exposed copper is removed. The gold-masked areas assume theshapes of the conductive strips, the annular rings about the apertures,and the coating on the aperture walls. In most etching operations ofthis nature, under-cutting by he etchant is undesirable in that itremoves copper that should be permitted to remain. However, in thisinvention the undercutting is operator-controlled, and exploited to anadvantage and developed as a desirable feature. Referring now to FIG. 5athere is seen an exploded portion of the coating as it appears on theaperture walls and upper and lower card planar surfaces immediatelyafter the completion of the coating step. There can be seen aninsulation layer 22, a layer of copper 43, and a layer of gold 44superimposed on the layer of copper.

FIG. 5b illustrates the card immediately subsequent to the abrasion ofthe underside of the card. There it is seen that the layer of gold 44has been removed on the undersurface of the card along with a smallportion of the copper layer 43. lt will be appreciated by those skilledin the art that when the underside of this card is exposed to a ferriechloride etchant, the etchant will immediately attack the copper layer43. In the area of the aperture 24, this will result in the removal ofcopper to which the `gold layer 44 is attached and the gold attached tosuch copper will fall away exposing the base material within theaperture. The use of a thin film of gold as a resist in the methodtaught herein for practicing this invention is not to be construed as alimitation. One skilled in the art will appreciate that many otherorganic and inorganic resist materials may lbe employed and that suchresists may be applied in diverse ways.

Referring now to FIG. 5c it can be seen that the copper and gold havebeen removed from the underside of the layer 22, and a portion of theinsulation layer which forms the wall of the aperture has been exposed.As will be seen hereinafter, exposure of the base material within the.aper- 1ture 24 by etchant undercutting is advantageously utiized.

Step 4 is performed after the cards have been rinsed and allowed to dryand is initiated by assembling the cards in a stack. The cards arestacked such that the apertures of any one card are registered with theapertures of the next adjacent card. After the cards have been properlyregistered, they are secured in place by a guide pin or clamping means.Additionally, at this time a masking device or dam 38 is disposed aboutthe entire periphery of the stack. The dam may be constructed of anyheat resistance material that will lend itself to enclosing tightly atleast the bottom portion of the stack for preventing solder fromentering the space between the various layers forming the stack duringthe time that the stack of circuit cards is immersed in a solder bath.

After the masking device is iixed relative to the stack of circuitcards, step 5 is initiated. During this step a wicking means 36 isinserted from one side of the stack through each series of alignedapertures. The length of the wick is preferably such that its ends 37and 39 extend outwardly from the stack of circuit cards. The number ofwicks 36 that are inserted into a stack is generally equal to the numberof apertures 24 appearing in any single circuit card. Preferably thewicking means takes the form of stranded, fine copper wire which hasbeen found to produce the best capillary action. However, smalldiametered tubing has been successfully employed as a wicking means. Forexample, a copper plated, stainless steel tube having an outsidediameter of 0.015 inch has been utilized as a wicking means in apertureshaving a diameter of 0.016 inch. Solder readily ascends the Spaceavailable between the coating on the aperture Walls and the externaltube surface.

After all the wicks 36 have been properly inserted, step 6 isc-ommenced. The stack of circuit cards, for example, cards 22a, 22b, 22Cand 22d along with the wicking means 36 are immersed in a molten solderbath to a depth where the level of the molten solder 40 is substantiallyat the level of the uppermost surface 21 of the top circuit card of thestack. While the stack is immersed in the solder bath, the solderascends the wicks 36 and any space between the wicks and the coating onthe aperture walls by a combination of capillary action and displacementforces. The solder immersion step is continued until it is visuallydetermined that solder is present in each wick at the uppermost level ofthe printed circuit stack. When the operator determines that thesoldering operation is complete, the stack is removed from the bath andpermitted to cool at room temperature. After formation of the solderjoint 35 between the plated aperture walls and the wick, that portion 39of the wick which had previously been in direct contact with the solderis normally cut off and polished down such that the wick and thelowermost surface of the bottom circuit layer of the stack are ilush.

Referring now to FIG. 6, which illustrates a packaging scheme utilizinga stack of printed circuit cards joined in accordance with thisinvention, there is seen a plurality of logic circuit modules 52a, 521;,52C and 52d and an electrically insulating housing S3. The housing isdivided into quadrants 53a, 53h, 53C and 53d with each quadrant havingnine holes S8 therethorough. Eachr hole receives one of the connectorpins 60 which extend from the logic circuit modules in a predeterminedpattern for cooperating with the housing hole pattern. The pins areappropriately connected to electrical circuits (not shown) within theirrespective logic circuit modules.

A female connector 56 is affixed, for example by soldering or crimping,to each outwardly extending end portion 37 of the Wicks 36. Theconnectors 56 are also received by the holes 58 in the housing 53 andmate with the pins 60 in electrical engaging relationship. Two wicks 36'and 36 shown in phantom are electrically connected to a conductive strip59, also shown in phantom, by the method of this invention. The wicks 36and 36 are affixed respectively to connectors 56 and 56". When the logiccircuit block 52a is plugged into a multilayer assembly 54 pin 60 iselectrically received by connector 56', and when logic circuit block 52dis plugged in, pin 60" makes electrical contact with connector 56". Thusit can be seen that logic circuit blocks can be electrically connectedin a predetermined manner. For providing power and voltage signals tothe logic circuit blocks, a flexible cable 61 consisting of a thinisulating base 62 and a plurality of conductors 63 disposed thereon maybe used. The conductors may be connected to selected wicks, for example,by soldering.

it is understood that suitable modifications may be made in thestructure as disclosed provided such modications come within the spiritand scope of the appended claims. Having now, therefore, fullyillustrated and described my invention, what I claim to be new anddesire to pr-otect by Letters Patent is:

What is claimed is:

1. A multilayer circuit assembly comprising: a stacked plurality ofcircuit layers, each layer having an electrically insulating, solderrepellent base, and each of the layers having a plurality of aperturescoordinately arranged therein, the apertures of one of the layers beingaligned with the apertures of any other of the layers; a plurality ofconductive strips disposed on only one face of the base, the stripsterminating at predetermined apertures; a solderable coating covering aportion of the wall of each aperture, that end of the aperture wallopening on the nonconductor bearing face of the base being devoid ofcoating, the coating on the walls of the predetermined apertures beingelectrically connected to the strips terminating at the apertures; andan interconnecting wick member disposed through each ali-gned series ofthe apertures for causing capillary attraction of applied solder to forma continuous solder joint electrically connecting the member and thesolderable coating on each wall of the series.

2. A multilayer printed circuit assembly comprising: a plurality ofsuperimposed electrically insulating supports, each of said supportshaving lirst and second surfaces and each of the supports having aplurality of coordinately arranged apertures therethrough, the aperturesof one of the supports being aligned with the apertures of any other ofthe supports; a solderable coating covering a portion of the Wall ofeach aperture, that end of the aperture wall opening on the secondsurface of the supports being devoid of coating, at least one conductivestrip disposed on said first surface of each support, each end of saidstrip being connected to said solderable coating at a predeterminedaperture on said iirst surface for forming an electrical connectionbetween said aperture coatings, an annular ring of solderable materialon a surface of the support and surrounding each aperture, thesolderable coating and the solderable material being integral; and aninterconnecting wick member disposed through an aligned series of saidapertures and extending from the bottom on the superimposed supports tothe top thereof; said wick member causing capillary attraction ofapplied solder to form a single solder joint coupling the solderablecoating `on each aperture wall of the series with the interconnectingmember.

3. A multilayer circuit assembly comprising: a plurality of superimposedelectrically insulating supports each having iirst and secondplanarsurfaces, and each of said supports having a plurality of aperturestherein, the apertures of one of said supports being 'aligned with theapertures 4of any other of the supports; a solderable coating covering aportion of the wall of each aperture, that end of the aperture wallopening on the second planar surface being devoid of coating, conductivematerial disposed on only a iirst planar surface of each support andelectrically connecting said coating at predetermined apertures, aninterconnecting wick member disposed through an aligned series of theapertures for causing capillary attraction of applied solder andexten-ding from the bottom o-f the arranged superimposed suppor-ts tothe top thereof; stop means between each of the supports for preventingthe transverse flow of solder; and a continuous solder joint couplingthe solderable coating and the member.

4. A device as in claim 3 wherein the stop means includes an annularring on the iirst planar surface surrounding each aperture, the ringbeing disposed adjacent the secon-d planar surface of the next adjacentsupport in the circuit assembly.

5. A device as in claim 4 wherein the annular ring and the solderablecoating are integral.

6. A modularly arranged circuit system comprising: a multilayer circuitassembly including a plurality of sol- .der repellent insulatingsupports having first and second Opening on the second planar surface ofeach support is devoid of coating and at least one of the supportshaving disposed on only the first planar surface thereof a conductivestrip, the strip terminating at two of the apertures, one `of suchapertures being in the rst series of apertures and the other being inthe second series and being electrically connected to the solderablecoating covering the two aperture Walls; first and secondinterconnecting members, one being disposed in the first aligned seriesof apertures, the other being disposed in the second aligned series,each of the members having portions thereof extending outwardly from thestack; a rst continuous solder joint connecting the firstinterconnecting member to the solderable coating on each aperture Wallof the apertures forming the first aligned series of apertures; a secondcontinuous solder joint connecting the second interconnecting member tothe solderable coating on each aperture wall of the apertures formingthe second aligned series of apertures, the two interconnecting membersbeing electrically connected to the conductive strip by their respectivesolder joints; first and second connector elements respectivelyelectrically connected to the first and second `outwardly extendingportions of the interconnecting members; a circuit module havingelectrical circuits therein; first and second terminal pins electricallyconnected in a predetermined manner to the electrical circuits, thefirst and second terminal pins being releasably electrically connectedrespectively to the first and second connector elements for completingan electrical circuit including the conductive strip on the insulatingsupport.

7. A multilayer circuit assembly comprising: A stacked plurality oflayers of multiapertured electrically insulating supports having firstand second planar surfaces, the apertures being arranged in accord witha predetermined pattern and the apertures of one of the supports beingaligned with the apertures of any other of the supports; at least oneconductive strip disposed only on the first surface of each of -thesupports and terminating at predetermined apertures; a solderablecoating covering a portion of the Wall of each aperture, that end of theaperture wall opening on the second surface of each support being devoidof coating, said strip and said coating being integrally formed, aninterconnecting wick member disposed through each aligned series of theapertures for causing capillary attraction of applied solder to form asolder joint coupling the solderable coating on each aperture Wall ofthe series and the interconnecting member disposed through the series bycausing the strip to be electrically connected to the member, aninsulating housing having a plurality of holes therethrough; a pluralityot first electrical connecting members, each of the iirst members beingaixed to one ofthe interconnecting members and being supported in one ofthe holes in the insulating housing; a circuit block having a pluralityof electrical circuits; and a plurality of second electrical memberselectrically connected to the circuits Within the block and connectedWithin the housing to predetermined ones of the iirst members.

References Cited UNITED STATES PATENTS 2,734,150 2/1956 Beck 174-682,907,925 10/1959 lParsons 174-68 2,912,745 11/1959 Steigerwalt et al.174-68 2,700,150 1/1955 Wales 317-101 DARRELL L. CLAY, Primary Examiner.LEWIS H. MYERS, Examiner.

1. A MULTILAYER CIRCUIT ASSEMBLY COMPRISING: A STACKED PLURALITY OFCIRCUIT LAYERS, EACH LAYER HAVING AN ELECTRICALLY INSULATING, SOLDERREPELLENT BASE, AND EACH OF THE LAYERS HAVING A PLURALITY OF APERTURESCOORDINATELY ARRANGED THEREIN, THE APERTURES OF ONE OF THE LAYERS BEINGALIGNED WITH THE APERTURES OF ANY OTHER OF THE LAYERS; A PLURALITY OFCONDUCTIVE STRIPS DISPOSED ON ONLY ONE FACE OF THE BASE, THE STRIPSTERMINATING AT PREDETERMINED APERTURES; A SOLDERABLE COATING COVERING APORTION OF THE WALL OF EACH APERTURE, THAT END OF THE APERTURE WALLOPENING ON